Coherent photon beams generated by lasers usually exhibit Gaussian, centrosymmetric, intensity distributions in their conventional modes. The Gaussian, or bell-shaped, intensity profile of such beams limits their effectiveness in many applications.
For example, laser beams are used to treat various workpieces by heat-hardening, annealing, or vaporizing portions of the piece. Because of the bell-shaped intensity profile, beam power must be carefully controlled to prevent destructive, over-treatment of the workpiece; only the central portion of the beam can be used effectively. Thus, the workpiece must be exposed to a large number of narrow scans, which are time and power consuming.
Similarly, Gaussian beam profiles limit the effectiveness of laser beam usage in thermomagnetic optical memory recording; a "flat-topped" beam optimizes the amount of laser power passing through an isotherm without exceeding the destructive threshold on a recording medium. Additionally, a uniform laser beam profile can greatly enhance the performance of laser amplifiers because when the input beam to a laser amplifier has a Gaussian profile, only the central, axial portion of the amplifying medium is effectively used. A uniform-profiled beam can use the entire cross-sectional area of the amplifying cavity.
Moreover, uniform intensity-profiled laser beams are advantageous in optical radars which use detector arrays. A uniform intensity transmission beam will produce a more effective, stronger and more uniform returning far-field signal.
Various attempts have been made to produce uniform intensity beams, particularly uniform intensity laser beams. One period method involves reflecting a Gaussian-distributed laser beam off an array of tiny mirrors arranged to introduce a dispersing effect at the beam center. The obvious disadvantage of this method is the loss of beam coherence in the far-field. Nonetheless, this apparatus is useful in near-field applications, but costly to manufacture.
Another means to achieve uniform intensity laser beams, known in the art, involves passing the beam through an energy absorbing filter having a radial variation in absorbency or polarization. Disadvantages of this method are that energy is wasted in the filter and heat-dissipating auxilliary equipment is often required. Such techniques are very difficult and expensive to implement for non-radially symmetric distributions, often do not preserve polarization, and section the laser beam.
Therefore, there exists a need for a simple, cost effective and energy efficient means to convert Gaussian profiled beams into uniform intensity beams. More generally, there is a need for such a means for shaping any electromagnetic wave beam to a desired intensity profile.